[GRASSLIST:43] Re: Newbie Region Problems

[Paul Kelly]

On Thu, 15 May 2003, R. Sean Fulton wrote:

>
> Hello,
>
> I'm trying to combine some raster and vector data from
> www.pasda.psu.edu (links below). The raster (DOQ) and vector (SHAPE)
> are in different projections. I've created locations for each and
> imported them. When I re-project with v.proj (or r.proj) the two,
> which should overlap, are no where near each other.

Can you provide the output of the g.projinfo command for each location?
This shows the details of the projection parameters and perhaps there
might be something obviously wrong that somebody would be able to spot.
How far away do you mean by no where near each other (I assume not
overlapping at all?)

Other things that might be wrong are wrong units (feet/metres) (which
would give a large error), wrong datum (which would give an error of the
order of 100 metres), wrong false easting/northing offset (another large
error). You may change the parameters by directly editing the PROJ_INFO
and PROJ_UNITS files in the PERMANENT directory for your location.

> The region for the raster was set with info from gdalinfo and worked
> straight away, i.e. I could d.rast and see it. The vector files meta
> data had bounding coordinates that appear to be in lat/lon and so
> were useless for its projection (aea). Setting the region from the

You could convert them with m.proj2 from GRASS or (preferably) cs2cs from
the PROJ.4 distribution ( http://remotesensing.org/proj/ ).


> Are there any good primers on projections and grass regions and
> importing data? I couldn't find anything useful on the web-site.

I could try writing something about how projection is handled in GRASS,
although I don't really do much importing of ready-made datasets (there
aren't that many available for free in Europe) and so am unaware of the
type of problems people may face.

Paul Kelly